Coordination polymerization of olefinically unsaturated monomers is well known and has led to the great proliferation of thermoplastic compositions of matter from olefins, such as polyethylene, polypropylene, and ethylene propylene rubber. Early pioneers utilized the early transition metal compounds, particularly those of the Group 4 metals, with such activators as aluminum alkyl compounds. Later developments extended this work to bulky ancillary ligand-containing (e.g., .eta.5-cyclopentadienyl) transition metal compounds ("metallocenes") with activators such as alkyl alumoxanes. Representative work addressing polymer molecular weight effects of substituted mono and bis metallocene compounds is described in EP-A 0 129 368 and its counterpart U.S. Pat. No. 5,324,800. Hetero-atom containing monocyclopentadienyl metallocene compounds are described in U.S. Pat. No. 5,057,475 and silicon bridged biscyclopentadienyl metallocene catalysts are described in U.S. Pat. No. 5,017,714. Recent developments have shown the effectiveness of ionic catalysts comprised of activated metallocene cations stabilized by compatible noncoordinating anions, see for example U.S. Pat. Nos. 5,278,119 and 5,384,299 and WO 92/00333. Each of which is incorporated by reference for purposes of U.S. patent practice.
Transition metal polymerization catalyst systems from Group 5-10 metals wherein the active transition metal center is in a high oxidation state and stabilized by low coordination number polyanionic ancillary ligand systems are described in U.S. Pat. No. 5,502,124 and its divisional U.S. Pat. No. 5,504,049. Suitable low coordination number polyanionic ancillary ligands include both bulky imides and carbolides. Such are said to be suitable alone or in combination with conventional monoanionic ancillary ligands, such as cyclopentadienyl derivatives. Examples 2 and 8 illustrate Group 5 metal catalyst compounds comprising, respectively, (cyclopentadienyl)vanadium(p-tolylimido)dichloride and (cyclopentadienyl)niobium(2,6-diisopropyl-phenylimido)di-methyl. Olefin polymerization catalysts from Group 5 or 6 metal imido complexes are also described in EP 0 641 804. The Group 5 metal complexes include one imido ligand and a monoanionic organic group containing a cyclopentadienyl nucleus. Example 1 illustrates the preparation of (cyclopentadienyl)vanadium(p-tolylimido)dichloride and the Tables on pages 7-9 illustrate polymerization using it. These documents are incorporated by reference for purposes of U.S. patent practice.
Effective olefin polymerization catalysts based upon vanadium alkyl complexes in which the metal center is stabilized in its highest oxidation state are elusive since there are no well established procedures for the synthesis of such compounds. Difficulties associated with the synthesis of vanadium alkyls in which the metal center is stabilized in its highest oxidation state are well documented. See for example, Buijink, J. J. Organomet. Chem 1995, 497, 161-170, Devore, D. D. J. Am. Chem. Soc., 1987, 109, 7408-7416 and other references well known to those skilled in the art.
It would therefore be desirable to provide vanadium alkyl complexes in which the vanadium metal center is stabilized in its highest oxidation state by (a) a low coordination number polyanionic ligand and (b) and suitable additional ancillary ligands.